Regular and exotic behaviour

Traditional reaction kinetics has dealt with the large class of chemical reactions that are characterised by having a unique and stable stationary point (i.e. all reactions tend to the equilibrium ). The complementary class of reactions is characterised either by the existence of more than one stationary point, or by an unstable stationary point (which could possibly bifurcate to periodic solutions). Other extraordinarities such as chaotic solutions are also contained in the second class. The term exotic kinetics refers to different types of qualitative behaviour (in terms of deterministic models) to sustained oscillation, multistationarity and chaotic effects. Other irregular effects, e.g. hyperchaos (Rossler, 1979) can be expected in higher dimensions. 

Exotic chemical systems, mostly oscillatory reactions, but also systems exhibiting multistationarity and chaotic effects, have extensively been investigated. Phenomena in chemical, biological and industrial chemical systems are the experimental basis of the theoretical studies. 

For almost a century chemical kinetics used deterministic models only, which completely neglects the existence of fluctuations. However, at the same time the early thermodynamic fluctuation theory was already examining the quantitative aspects of the fluctuations. 

Since classical thermodynamics, including fluctuation theory, adopts continuous macroscopic variables, their fluctuations are described generally by Gaussian distributions. 

It is often mentioned that the stationary distribution of chemical reactions is generally the Poisson distribution (Prigogine, 1978). However, the significance of the Poisson distribution is rather limited other unimodal distributions can also reflect the regular behaviour of the fluctuating chemical sytems. Multimodality of the stationary distribution might be associated, at least loosely speaking, with multistationarity of deterministic 

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